Vehicle manufacturers are increasingly replacing mechanical linkages in vehicles with sensors and electromechanical devices to reduce weight and cost. For example, sensors are replacing mechanical linkages to detect positions of user operated devices such as accelerator, clutch, and brake pedals. Signals are transmitted from the sensors to controllers and/or electromechanical devices in the vehicle. For example, a signal from an accelerator pedal may be transmitted to an actuator in the electronic throttle body to adjust the position of the throttle blade. Additionally, a throttle position sensor detects the position of the throttle blade and transmits a signal to an engine control module.
In cases where mechanical linkages are at least partially eliminated, multiple sensors are commonly used to perform redundant measurements and ensure system accuracy. For example, some manufacturers use analog position sensors that are based on a resistive ink or paste that is deposited on a non-conducting substrate. Other manufacturers use application specific integrated circuits (ASICs) in combination with sensors. The sensors typically include hall effect or inductively coupled sensors. The ASICs receive analog signals from the sensors and output pulse width modulated (PWM) or other types of signals.
Referring to FIG. 1, a vehicle control system 10 includes a throttle body 12 and a control module 14. The throttle body 12 includes first and second sensor modules 16 and 18, respectively, that communicate with the control module 14. The throttle body 12 also includes a throttle blade 20 that is in mechanical contact with the sensor modules 16 and 18. The sensor modules 16 and 18 are potentiometer-based sensors 16 and 18 that include adjustable sensor resistances. During normal operations, the throttle blade 20 moves between a minimum position and a maximum position. For example, the minimum position may be an idle throttle position, and the maximum position may be a wide-open throttle (WOT) position. As the throttle blade 20 moves between the minimum and maximum positions, mechanical contacts 22 between the throttle blade 20 and the sensor modules 16 and 18 adjust the values of the sensor resistances.
The first and second sensor modules 16 and 18 generate first and second position signals 24 and 26, respectively, based on the values of respective sensor resistances. The sensor modules 16 and 18 transmit the position signals 24 and 26 to the control module 14. The control module 14 determines first and second positions of the throttle blade 20 based on values of the position signals 24 and 26. For example, the control module 14 may store values of the position signals 24 and 26 when the throttle blade 20 is set at predetermined positions during a calibration process. This allows the control module 14 to determine the values of the position signals 24 and 26 by scaling between the preset values. The multiple positions of the throttle blade 20 allow the control module 14 to perform redundancy testing and to verify the integrity of the sensor modules 16 and 18.
In the event of an electrical short-circuit between the first and second sensor modules 16 and 18, respectively, one or both of the values of the position signals 24 and 26 may become invalid, which adversely affects vehicle control. In one approach, the first sensor module 16 includes a short-circuit switch 28. When activated by the control module 14, the short-circuit switch 28 sets the value of the first position signal 24 to a predetermined value. For example, the value of the first position signal 24 may be set by shorting the sensor resistance of the first sensor module 16 to a reference or ground potential. While the short-circuit switch 28 is activated, the control module 14 compares the values of the first and second position signals 24 and 26, respectively. If the difference between the values of the position signals 24 and 26 is less than a predetermined value, it is likely that a short-circuit condition exists between the sensor modules 16 and 18 and the control module 14 may activate an alarm indicator.
The short-circuit switch 28 allows the control module 14 to periodically detect a short-circuit condition between the sensor modules 16 and 18. However, the accuracy of the position signal values are compromised while the short-circuit switch 28 is activated. This interrupts other system diagnostics that utilize the values of the position signals 24 and 26 from the sensor modules 16 and 18. Additionally, the short-circuit switch 28 provides added cost and complexity to the sensor modules 16 and 18.